Fig. 7.—The view ahead.
Fig. 8.—The view astern.
Airplane Instruments.—Mounted on boards in front of the pilot and observer are various instruments to indicate the performance of engine and plane (Fig. [2]). Those of interest to the photographic observer are the compass, the altimeter, the air speed indicator, the inclinometers.
Fig. 9.—The view between the wings.
Fig. 10.—Appearance of the earth from a low altitude—3000 feet or less.
The compass is usually a special airplane compass, with its “card” immersed in a damping liquid. Like most of the direction indicating instruments on a plane its indications are only of significance when the plane is pursuing a steady course. On turns or rapid changes of direction of any sort perturbations prevent accurate reading.
The altimeter is of the common aneroid barometer type. On American instruments it is usually graduated to read in 100-foot steps. While somewhat sluggish, it is quite satisfactory for all ordinary determinations of altitude in photographic work. Were primary map making to be undertaken, where the scale was determinable only from the altitude and focal length of the lens, the ordinary altimeter is hardly accurate enough.